1. Field of the Invention
The present invention relates to an image processing apparatus and program for arterial evaluation in an X-ray computed tomography apparatus (CT apparatus) or magnetic resonance imaging apparatus (MR apparatus), an X-ray angiography apparatus, an ultrasonic apparatus, an IVUS apparatus, or an OCT apparatus and, more particularly, to an image processing apparatus and program which are used to evaluate arterial atherosclerosis.
2. Description of the Related Art
For example, coronary arterial atherosclerosis mainly involves atherogenesis, lumen stenosis, arterial wall remodeling, and the like. Conventional methods of evaluating these phenomenon include coronary angiography (CAG), an ultrasonic apparatus, a coronary artery endoscopy, intravascular ultrasound (IVUS), and optical coherence tomography (optical CT or OCT). However, they are all invasive examination methods. In particular, these invasive diagnostic procedures have a risk of developing serious complications including death at the time of examination, and hence are not always safe. For this reason, the certain candidate for these examinations are limited to patients expecting percutaneus coronary intervention (PCI) for treatments and IVUS should not be used for patients with high risk to perform. In addition, evaluation of narrowing lumen (lumen stenosis) using coronary angiography (CAG) or an ultrasonic apparatus, which has been conventionally performed, is measurement on a projection image of arterial lumen, and hence leads to underevaluation.
With the advent of multislice CT, contrast enhancement CT examination has been expected as noninvasive, useful examination. The examination data have been used to measure the ratio of arterial lumen and wall, remodeling indices, and clinical applications of this technique have begun to be studied.
In this case, the ratio of lumen stenosis can evaluate a vascular lumen state but cannot evaluate a remodeling state which has recently been considered important in the process of development of arterial atherosclerosis. In contrast, a remodeling index cannot properly evaluate a lumen stenois state. In addition, both the techniques are designed to compare with a reference region, and hence must set a reference region. Furthermore, reference regions might be derived from diffuse arterial atherosclerotic region, misleading to inadequate results.
In order to evaluate atherogenesis by using a CT apparatus, mural evaluation based on CT values is performed. However, owing to the influence of a contrast medium concentration, the limitation of a spatial resolution in currently available apparatuses, and the like, this evaluation is local evaluation and is not used to evaluate the overall target artery.